1. Field of the Invention
The invention relates to a covering device with a cover member which selectively opens and closes by means of a pair of hinge units, and to an image reading apparatus equipped with the covering device and an image recording apparatus equipped with the image reading apparatus.
2. Description of the Related Art
Image reading apparatus provided in copying machines are known. A known image reading apparatus is provided with a cover member which is configured to cover and press a document placed on a reading glass plate. The cover member is attached to one side of a lower casing of the image reading apparatus by a pair of hinge units. The known image reading apparatus reads an image of the document placed on the reading glass plate. The known image reading apparatus also reads images in a book, such as a bulky book. When reading images in a bulky book with the image reading apparatus, the cover member for covering the book document is moved orthogonally, e.g., vertically, to the wide surface, e.g., a horizontal surface, of the reading glass plate by means of a pair of hinge units. The known image reading apparatus has been proposed in Japanese Unexamined Patent Application Publication Nos. 2007-228528 and 2007-228529. The lower casing is attached to an upper surface of a housing accommodating an image recording unit in a multifunction apparatus or the like.
Specifically, as disclosed in a known image reading apparatus, e.g., the apparatus disclosed in Japanese Unexamined Patent Application Publication Nos. 2007-228528 and 2007-228529, and, as shown in FIGS. 19A and 19B, a reading glass plate is attached to an upper surface of a lower casing 101 of an image reading apparatus. The image reading apparatus is mounted on top of a housing 100 of a multifunction apparatus or the like. A linear image reading unit (not shown) is disposed below the reading glass plate. A partial casing 103 protrudes upwardly from the upper surface of a cover member 102 and covers the entire upper surface of lower casing 101. An auto document feeder for feeding a document is built into partial casing 103. In addition, a document tray unit 104 is provided. Document tray unit 104 slopes downwardly toward partial casing 103. Further, documents stacked on the document tray unit 104 are conveyed and separated one from another by the auto document feeder. Documents are then scanned by the image reading unit and discharged to a discharge tray unit 105 disposed on the upper surface of cover member 102 below document tray unit 104. An image of the document placed on the reading glass plate is read by the image reading unit moving along the lower surface of the reading glass plate.
Furthermore, in order to read an image in a bulky book while pressing the bulky book with cover member 102, a pair of hinge units 106 and 107 are provided on the rear side of lower casing 101. Cover member 102 is attached to the casing by hinge units 106 and 107 in such a manner that cover member 102 is vertically movable relative to the upper surface of the reading glass plate.
As shown in FIG. 19A, the pair of hinge units 106 and 107 are arranged such that a first hinge unit 106 is positioned further away from partial casing 103 than a second hinge unit 107. Bearing portions provided at the upper end of a hinge block member 106a of first hinge unit 106 and a hinge block member 107a of second hinge unit 107 are coupled to one side of cover member 102 through horizontal rotating shafts, respectively. The elongated hinge block members 106a and 107a are accommodated in storage units 106b and 107b in lower casing 101 in a vertically-movable, e.g., slidable, manner.
In a known image reading apparatus, e.g., the image reading apparatus disclosed in Japanese Unexamined Patent Application Publication Nos. 2007-228528 and 2007-228529, however, a problem occurs when cover member 102 pivotally opens to expose the reading glass plate for setting the document thereon. More specifically, upper partial casing 103 of cover member 102 incorporates various mechanical parts, such as, a pickup roller, a feed roller, and a guide member for conveying the document constituting the auto document feeder. In FIGS. 19A and 19B, the center of gravity Go of the weight W of cover member 102 is positioned on the left side, i.e., closer to second hinge unit 107 than first hinge unit 106.
A horizontal groove-like recess portion 108 is formed on another side of cover member 102, e.g., opposite to the side where the pair of hinge units 106 and 107 are disposed. When an operator puts his/her fingers into recess portion 108 to open cover member 102, first hinge unit 106, which is further from the center of gravity Go, has a load lower than a load of second hinge unit 107, which is closer to the center of gravity Go. Thus, as shown in FIG. 19B, hinge block member 106a moves upward and off storage unit 106b to raise the right side of cover member 102 before the left side of cover member 102 is lifted up. As a result, displacement occurs between right hinge unit 106 and left hinge unit 107. The displacement causes cover member 102 to not pivotally open in a smooth manner.